Asthma affects nearly 10% of American children, resulting in treatment costs alone in excess of $3 billion annually. Asthma is highly correlated with obesity and quality of nutritional in multiple cross-sectional studies, although the mechanism of this association remains speculative. Limited interventional studies in adults with asthma, relying on behavioral modification, report improvements in asthma control with caloric restriction and diets enriched with antioxidants and omega-3 fatty acids. Low glycemic index and high fiber diets may decrease systemic inflammation, according to observational analyses and feeding studies, but this dietary strategy has not been investigated in this population. A diet harnessing the anti-inflammatory properties of multiple foods may improve pulmonary function, yet this strategy remains largely untested, especially in children. The specific aim of this projec is to evaluate the effects of a diet that is low in glycemic load and abundant in fiber, fruits, vegetables, legumes and omega-3 fatty acids (identified in this proposal as the anti-inflammatory diet) on pulmonary function in lean and overweight pediatric patients with asthma. The primary endpoint will be change in forced expiratory volume in one second in response to the diet intervention. Secondary outcomes will include additional spirometry measures, fraction of exhaled nitric oxide, and assessment of symptomatic asthma control. In addition, we will identify potential physiological mechanisms relating diet with lung function, including changes in systemic and adipose-specific inflammation, insulin sensitivity, and intestinal microbiome composition. Forty patients, age 10-18 years, with moderate to severe persistent asthma will be randomized to receive an anti-inflammatory diet versus habitual diet for 6 weeks, with crossover to the opposite diet for an additional 6 weeks. Both diets will be isocaloric and weight maintaining, to isolate the effects of the dietary composition from the known beneficial effects of weight loss. During the intervention period, meals will be delivered directly to subjects' homes through a novel collaboration with LYFE Kitchen (Chicago, IL), maintaining careful control of macro- and micronutrient content. During the habitual diet, participants will consume self-prepared meals. If successful, this study will contribute to a mechanistic understanding of asthma, and could inform the development of a novel, safe and easily translatable approach to asthma management. Future studies would 1) confirm the results in larger and more heterogeneous populations; 2) translate findings into sustainable interventions and 3) further explore the underlying mechanisms relating dietary intervention to lung function.